The present invention relates to a plasma processing method and more particularly, to a method of etching a magnetic film.
In recent years, with a view to dealing with an increase in storage capacity of a hard disk drive, a used technology is shifting from the giant magneto resistive (GMR) to the tunneling magneto resistive (TMR) and its surface recording density is rapidly increasing. Accordingly, miniaturization of a magnetic head used for the hard disk drive has been required and a technique for fine pattern etching of the magnetic head has been demanded. Therefore, a dry etching apparatus is being used more than an ion milling apparatus for fabrication of the magnetic head.
A magnetic film constituting the magnetic head is made of a nonvolatile material such as NiFe, CoFe, or CoNiFe. But since the nonvolatile material has a very low volatility, which makes a high etching rate and a vertical profile not easily obtained, its fine pattern etching is difficult. Also, a reaction product created during etching will deposit on the inner wall of a processing chamber, often causing a change in time in etching performance to occur.
In order to realize fine pattern etching of the magnetic film made of the nonvolatile material with the current status of the dry etching technology as described above, various conditions such as etching gases and mask materials used in etching of magnetic films have been considered. For example, JP-A-2005-42143 discloses that using alcohol as etching gas for magnetic films high selectivities to mask materials can be obtained and JP-A-11-92971 discloses that NH3 and CO are used as etching gas for magnetic film. In these methods, however, the etching rate is low to bring about poor productivity. Furthermore, since alcohol, NH3, or CO are not used normally as the etching gas for the nonvolatile film, safety equipments such as leak detectors and hazard preventive equipments need to be newly facilitated for using these gases and additional costs would incur. For these reasons, in order to dry-etch a magnetic film of 100 nm or more with chlorine gas, which is normally used, as a primary gas, JPA-2010-49761 discloses a method in which dry etching of a magnetic film is carried out using a mask material having a boiling temperature of its chloride higher than that of a chloride of a magnetic film material.
More particularly, on a CoFe magnetic film having a thickness of about 250 nm, a mask of a multilayered film composed of an Al2O3 film 15, a Cr film 14, and a patterned resist film 11 is formed as shown in FIG. 2A. Initially, the Cr film 14 is etched with a mixture gas of chlorine and oxygen using the resist film 11 as a mask, the Al2O3 film 15 is etched subsequently with boron trichrolide gas, and finally, the CoFe Film is etched with a chlorine gas. In addition to Al2O3 and Cr, materials such as Ru, Mn, Pd, Y, Nd, Pr, Ce, La, Y2O3, Nd2O3, and CeO2 can be enumerated as the mask material. But in dry-etching of the magnetic film with chlorine gas as a primary gas using the multilayered film of the above mask materials and the resist film 11, fine pattern etching in the vertical direction is difficult to achieve for the following reason. In conducting etching of the Cr film 14 using the mixture gas of chlorine and oxygen, the resist film 11 constituting the mask for the Cr film 14 has a principal component of carbon, which easily reacts with oxygen, and is therefore easily etched. Then, the resist film 11 is etched progressively in longitudinal and lateral directions as shown in solid line in FIG. 2B and the Cr film 14 is tapered in profile. This tapered profile of the etched Cr film affects etching profiles of underlying layers progressively and processing of the magnetic film into desired dimensions becomes difficult. For the purpose of etching the magnetic film of 200 to 500 nm at a high etching rate, using as the mask the multilayered film of Al2O3 film 15 and Cr film 14 which can have a high selectivity for the magnetic film as described in JP-A-2010-49761 is essential but with such mask of multilayered films, a excellent fine pattern etching profile is difficult to obtain as discussed above.